23.7.56 Predefined_Numeric_Types

Flag each explicit use of the name of any numeric type or subtype defined
in package Standard.

The rationale for this rule is to detect when the
program may depend on platform-specific characteristics of the implementation
of the predefined numeric types. Note that this rule is over-pessimistic;
for example, a program that uses String indexing
likely needs a variable of type Integer.
Another example is the flagging of predefined numeric types with explicit
constraints:

This rule detects only numeric types and subtypes defined in
Standard. The use of numeric types and subtypes defined in other
predefined packages (such as System.Any_Priority or
Ada.Text_IO.Count) is not flagged